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  • TRAINING SECTOR GENERAL DEPARTMENT FOR

    PLANNING & DEVELOPING PROGRAMS

  • Contents

    - GSM Introduction

    - CDMA Overview

    - GPRS Introduction

    - UMTS Introduction

    - HSDPA for WCDMA

  • TRAINING SECTOR GENERAL DEPARTMENT FOR

    PLANNING & DEVELOPING PROGRAMS

  • Sub-sections

    GSM Introduction

    Introduction 1

    Transmission Principles 2

    GSM PLMN 3

    Procedures 4

    Radio Interface 5

    Appindex 6

  • GSM Introduction

    Sub-section reference

    Sub-section identification Pages1 Introduction 1 - 44 2 Transmission Principles 1 - 37 3 GSM PLMN 1 - 32 4 Procedures 1 - 38 5 Radio Interface 1 - 31 6 Appendix 1 - 14

    This document consists of 196 pages.

  • Chapter 1

    Introduction

  • Introduction

    Introduction

    Contents

    2History 1 15 GSM 2 27Current Situation, Market & Trends 3

  • Introduction Siemens

    1 History

    Introduction

    History

    Fig. 1

    2

  • Siemens Introduction

    History of Mobile Communications

    Mobile Communication is much older than many people think. There have beendiverse "acoustic and optic means of remote information transfer" in the most variedcultures and stages of civilization on all populated continents. The range ofinformation transfer was very limited and the quality of the messages was affected byouter conditions such as the weather. In order to increase the range of informationtransfer in these times, transit stations were in part systematically constructed.

    Beginnings of Electronic Communications

    Telegraph: S.F.B. Morse: 1843 First experimental telegraph line: Washington -Baltimore

    Telephone: Phillip Reis 1861: First speech transmission by cable / A. G. Bell: 1876World Exhibition, Philadelphia

    At first electronic communications was possible only via wire i.e. by means of fixed(immobile) connections, forerunners of today's Fixed Network Connections. Initiallyan operator ("switchboard girl") was needed to establish these fixed physicalconnections for the caller manually at the central office. The first automaticexchanges were first put into service in the mid-1920s.

    Radio Communications

    Radio connections were first used for Wireless Communications in the late 19thcentury; information was sent via "ether".

    1873: J.C. Maxwell - electromagnetic wave theory

    1887: H. Hertz - experimental proof of the existence of electromagnetic waves

    1895: A. Popow - first receiver with antenna for weather reports

    1895: G. M. Marconi - first wireless transmission using spark inductor generatedHF waves (Morse code)

    1897: Marconi Wireless Telegraphy Company" founded

    1901: First transatlantic transmission (Marconi)

    1903: "Deutschen Telefunken GmbH" founded by AEG and Siemens & Halske

    1906: First speech & sound transmission (Lorenz AG / Deutsche TelefunkenGmbH)

    1909: First radio broadcast (New York, Caruso)

    3

    Introduction Siemens

  • Introduction Siemens

    The beginnings: "archaic mobile communication"

    visual transmission (smoke/light signals,...)

    audible transmission (drums, horns,...)

    Electronic

    communication:

    "terrestrial network"

    Telegraph 1st telegraph line 1843

    Washington - Baltimore

    Telephone

    P. Reis 1861 A.G. Bell 1876 World Exhibition Philadelphia

    Radio transmission:1873 Maxwells theory of electromagn. waves

    1887 H. Hertz: experimental proof1895 Marconi: 1st wireless transmission1901 1st transatlantic transmission

    1903 Dt. Telefunken GmbH: AEG, Siemens& Halske1906 1st speech and sound transmission1909 1st radio broadcast

    1917 1st mobile transmission: radio station - train

    History of Mobile Communications

    Fig. 2

    4

  • Siemens Introduction

    Connection Types

    There are two principles for radio connections:

    Simplex Connection

    Simplex connections are a "one-way street" for communication in the form of (mostlyfixed) transmitters and mobile receivers. This has been realized as e.g. (broadcast)radio and television. But simplex connections are also used for direct communicationexchange i.e. two-way communication using stations which can be used both as atransmitter and a receiver (e.g. walkie-talkies). However the equipment (transmitting /receiving stations) cannot transmit and receive simultaneously. The call cycles or callintervals are determined by prior agreement or personal code words ("over").

    Duplex Connections

    Duplex connections signify two-way communication. Users can transmit and receivemessages simultaneously. An example of an early duplex connection is radiotelegraphy.

    Simplex Connection:transmit or receive

    Duplex Connection:simultaneous

    transmission and reception

    Over

    Fig. 3

    5

    Introduction Siemens

  • Siemens Introduction

    Single Cell Systems

    The first Mobile Telephone Service to offer duplex connections comparable to fixednetwork based telephone services started in 1946 as a car phone service in St.Louis, Missouri. Comparable mobile telephone services appeared in post-war Europesome years later.

    Problems in early mobile (car) telephone services (late 1940s/early 1950s):

    An operator was needed to connect calls within the wireless network.

    The equipment required was extremely heavy, bulky (therefore only feasible as acar phone service) and expensive.

    The service range was limited to the area that could be covered by a singletransmitting or receiving station (single cell system).

    The HF frequency range available was (is) very limited; it had to be (and still hasto be) distributed among competitors (e.g. the military, radio, and television).

    The result was limited capacity, rapid market saturation, high equipment costs andlow service quality.

    Car telephone service

    Since the late 40s

    Low service and speech quality

    Heavy, bulky and expensive equipment

    Small coverage area

    No handover

    Manual exchange

    Low capacity

    First Mobile

    Services:

    Single Cell Systems:

    Fig. 4

    6

    Introduction Siemens

  • Siemens Introduction

    Innovations in Mobile Radio Communications

    Technical Innovations / Equipment

    Fast development of new technologies such as semiconductor technology, diodes,transistors, integrated circuitry, microprocessors,...

    automatic switching

    reduction of hardware costs

    reduction of size and weight of equipment (in the 1950s/1960s a car phone tookup half of a car trunk; 1988: introduction of the mobile phone)

    but:

    very limited telephone network capacity.

    During the 1970s large-scale integrated, electronic applications and the developmentof microprocessors made the configuration of more complex systems possible. Oneresult of this was the development of single-cell transmitter systems with multiplereceiving stations. This made it possible to extend the range of the supply area, i.e.the operational range of the subscriber because the mobile station's transmitterpower limits the size of the cell in Single Cell Systems. However no increase incapacity resulted from this.

    Cellular Mobile Radio Systems

    The breakthrough in capacity, which resulted in a significant increase in the numberof subscribers, was achieved with the introduction of the Cellular Radio System in thelate 1970s/early 1980s. The coverage of the supply area of a mobile communicationoperator involves many radio cells with cellular radio systems, in which theaforementioned limitation of the available HF frequency range is neatly circumventedthrough the repeated use of the HF channels.

    7

    Introduction Siemens

  • Introduction Siemens

    Quantum Leap in Mobile Communications:

    Single Cell Systems Cellular Systems

    radius

    r

    re-use distance

    r

    Single Cell

    System

    Cellular

    System

    Fig. 5

    8

  • Siemens Introduction

    First Generation (1G) Cellular Mobile Radio Systems

    Information transmission of first generation cellular mobile radio system takes placevia analogue radio interface. These systems were tested in many countries in the endof the 70s.

    In 1979, mobile services were introduced for commercial operation; in the USA,AMPS (Advanced Mobile Phone Service), and in Japan, NTT-MTS (NipponTelegraph & Telephone Co.).

    In the early 80s, the NMT (Nordic Mobile Telephone) was introduced in Scandinavia,in 1985 TACS (Total Access Communication System) was introduced in England andthe C450 System in Germany.

    First Generation Cellular Mobile Radio Systems

    Country System Frequency range[MHz]

    Introduced

    in year

    USA AMPS 800 1979

    Japan NTT-MTS 800 1979

    Sweden, Norway,Finland, Denmark

    NMT 450, 900 1981 - 86

    Great Britain TACS 900 1985

    Germany C450 450 1985

    France Radiocom2000

    NMT

    450

    900

    1985

    1989

    Italy RTMS

    TACS

    450

    900

    1985

    1990

    Fig. 6

    9

    Introduction Siemens

  • Siemens Introduction

    Second Generation (2G) Cellular Mobile Radio Systems

    A further and very significant innovation in mobile radio communications took placewith the introduction of the second generation cellular mobile radio system (e.g.GSM) in the early 90s. Transmission via radio interface is now digital. Along with asignificant improvement of transmission quality and expansion of services, there hasbeen a considerable increase in capacity. The increase in subscribers led to moreconvenient, lighter and less expensive equipment with a wide range of possibilitiesfor use.

    Portable Mobile Equipment

    Mobile phones were first introduced in 1988. The weight of the equipment decreasedfrom 1 kg to less than a

    100 g within few years. At the same time, mobility clearly improved despitedecreasing weight owing to improvements in rechargeable batteries. Standby timesof more than 5 days can be achieved.

    2nd Quantum Leap:

    Analog (1st Generation) Digital (2nd Generation)

    Different Generations of Mobile Stations

    Second generation

    GSM mobile telephones Second generationGSM mobile telephones

    Digital GSM technology.Terminal devices are handier

    and have greater battery capacity.

    Digital GSM technology.Terminal devices were less

    bulky, but still too heavy(battery capacity problems).

    Analog technology.Terminal devices were

    bulky and heavy.

    First generation

    mobile telephones

    for fixed vehicle installation and

    analog mobile telephones

    Fig. 7

    10

    Introduction Siemens

  • Siemens Introduction

    Example: Mobile Subscriber in Germany

    Since the early 50s there have been several regional networks at 30, 80, 100 MHz.They were allocated only to public authorities and organizations with security tasks.The regional networks (DBP) were combined in the so-called A-network in 1958 al-lowing private use for the first time.

    A-network: in operation: 1958 - 1977; frequency range: 156 - 174 MHz; in thebeginning 16, later 37 radio carrier; analogue transmission, manual switching; max.11,000 users (1971); closed in 1977; its frequencies were transferred to the B-network.

    B-network: in operation: 1972 - 1994; frequency range: 146 - 164 MHz; from 1977 to174 MHz (from A-network); in the beginning 38, later 75 radio carrier; analoguetransmission, automatic switching; max. 27,000 users (1986); problem: max.capacity, no further channels; closed in 1994.

    C-network (C450): in operation: 1985 - 2000; frequency range: 451.3 - 455.74 MHz& 461.3 - 465.74 MHz; 222/287 radio charier; system technology: Siemens. TheC450 system was the first German cellular system and led to an enormous increaseof subscribers (max. 850,000 users). The C-network was similar in structure tomodern digital networks.

    D-networks (GSM900): Introduction in 1992 (D1 & D2); 900 MHz frequency range (+minor extensions in the 1800 MHz range from 1999 on; system technology partlyfrom Siemens (D900).

    E-networks (GSM1800): Introduction in 1994 (Eplus) and 1998 (E2); 1800 MHzfrequency range; System technology partly from Siemens (D1800).

    The digital D and E networks, being GSM900 / GSM1800 networks, led to a rapidand steady increase of the number of subscribers in Germany. In 12/2000, a total of46 million mobile subscribers were registered in the 4 networks, D1, D2, Eplus & E2.

    11

    Introduction Siemens

  • Introduction Siemens

    0,01

    0,1

    1

    10

    100

    Su

    bs

    cri

    be

    r [M

    .]

    1978

    1980

    1982

    1984

    1986

    1988

    1990

    1992

    1994

    1996

    1998

    2000

    Year

    Germany

    Subscriber trends (Example): Germany 1978 - 2000

    B-n

    etw

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    in

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    Fig. 8

    12

  • Siemens Introduction

    Limits of the First Generation Mobile Radio Systems

    1. Capacity: The capacity limits of analogue technology are reached quickly evenwith cellular networks. The demand increases with the offer and the sinkingprices. A number of 850,000 subscribers, i.e. the maximum capacity of theanalogue C-network, corresponds to less than 7 % of the mobile subscribers in1998 (only 6 years after introducing digital networks). The capacity of digitalnetworks has not yet been exhausted.

    2. Quality: A second problem was the often inadequate transmission quality of theanalogue systems, which increased with the distance of the mobile subscriber. Adetailed description and discussion of the problems regarding the transmissionquality or the disadvantages of the analogue system in comparison to digital onecan be found in the next chapter.

    3. Incompatibility: One or more analogue networks on frequency bands 450/900MHz existed in most European states in the late 1980s. Every one of thesenetworks formed a mobile communication island since the individual standards ofthese networks were incompatible in most cases (or still are, as far as they stillexist); they prevented mobile phone traffic across borders (InternationalRoaming). Europe thus looked liked a rag rug of incompatible systems.

    The limits of existing analogue systems

    1. Capacity: the number of potential mobile phone customers is larger than theexpected capacity of analogue systems,

    2. Quality: insufficient transmission quality with increasing distance between themobile station and the base station,

    3. Incompatibility: between different national standards,

    were already recognized since the early 80s and were discussed on an internationalEuropean level. The need to develop a new, standard cellular system for Europe wasacknowledged.

    The GSM Standard was developed for this purpose.

    13

    Introduction Siemens

  • Introduction Siemens

    Capacity Quality Incompatibility

    European mobile

    communication marketearly 90s

    1G Limitations

    Fig. 9

    14

  • Introduction Siemens

    2 GSM

    Introduction

    GSMGlobal System for

    Mobile Communications

    Fig. 10

    15

  • Siemens Introduction

    The GSM History

    The foundation for the GSM Standard was laid already in 1978, four years before thename GSM was established. In 1978 the CEPT reserved a frequency range round900 MHz for mobile communications in Europe. The limits of analog mobilecommunications in Europe were recognizable in the early 80s. At that time the firstanalog cellular networks were just beginning their operation and were still far fromtheir maximum capacity. Despite this a group of experts was formed to establish thelonger-term challenges of mobile communications and to develop a new bindinginternational standard for digital mobile communications in Europe. Thus the GSMStandard became undoubtedly one of the most successful European products of thepast decades; its sphere of influence is extended far beyond the originally plannedEuropean scope.

    Milestones of the GSM Standard

    1982: The CEPT forms a team of experts, the Group Special Mobile (GSM) withthe purpose of developing a binding international standard for mobilecommunications in Europe.

    1984 86: Various technical possibilities are compared in order to achieve anoptimal utilization of the predefined frequency ranges.

    1986: A permanent core of experts is employed.

    1987: Main transmission principles are selected; 13 countries agree in the MoU(Memorandum of Understanding) to start GSM networks until 1991.

    1988: The ETSI (European Telecommunication Standards Institute) is founded;most of the standardizing activities of the CEPT, including GSM, are assumed bythis new body. Along with state-owned operators, industry, private networkoperators and consumer groups participate in the ETSI, too.

    1989: GSM is renamed from "Group Special Mobile" to "Global System for MobileCommunications".

    1990: GSM900 Standard (Phase 1) is adopted. DCS1800 Standard (Phase 1) isdeveloped as first GSM adaptation. The first GSM systems are in test operation.

    1992: Commercial introduction of many large GSM900 networks.

    1993: Work begins on updating the GSM900/DCS1800 standards: GSM Phase 2.

    1995: GSM-R (Railway): The ETSI reserves further frequency range for a railwaynetworks; first test projects are started. GSM Phase 2 work is completed.

    1996: Worldwide success of GSM Standard; used in more than 50 countries.PCS1900 (Public Cellular Systems) as further GSM adaptation in the USA.

    16

    Introduction Siemens

  • Introduction Siemens

    GSM Milestones

    1978 CEPT reserves 2 x 25 MHz in 900 MHz range

    1982 CEPT founds "Groupe Special Mobile" GSM

    1984-86 Comparison of technical possibilitiesGoals: - free roaming

    - international accessibility under 1 number (international roaming)- large network capacity (bandwidth efficiency)

    - flexibility ISDN- broad service offering- security mechanisms

    1986 Core of experts meets continuously

    1987 Selection of central transmission techniques

    Memorandum of Understanding: MoU

    1988 ETSI founded

    1989 GSM Global System for Mobile Communication

    1990 GSM900 Standard (phase 1)

    1991 DCS1800 adaptation

    Trials / "friendly user" operation

    1992 Start of commercial operation

    1993 Beginning of work on phase 2

    1995 Completion of work on phase 2 (GSM900/DCS1800)

    Reservation of GSM-R frequencies (ETSI)

    1996 PCS1900 adaptation (USA)

    Fig. 11

    17

  • Siemens Introduction

    1997: GSM Phase 2+ Annual Release 96: CAMEL Stage 1, ASCI for GSM-R.DCS1800 / PCS1900 are renamed to GSM1800 / GSM1900. Dual bandequipment for GSM900 / GSM1800; 10 years of MoU: 109 countries; 239operators; 44 million GSM subscribers; 28 % share of the world market.

    1998: Phase 2+ Annual Release 97: HSCSD, GPRS Stage 1, CAMEL Stage 2,...08/98: 100 million GSM subscribers in 120 countries; 35 % share of the worldmarket; GSM is quasi world standard. GSM-R networks in operation. World-wideservicing through co-operation with mobile satellite systems (IRIDIUM).

    1999: Phase 2+ Annual Release '98; 250 million subscriber; 130 countries

    2000: Phase 2+ Annual Release '99: GPRS Stage 2, CAMEL Stage 3, EDGE,Virtual Home Environment VHE, Adaptive Multirate speech AMR,...GSM Rel. '99services identical to UMTS Rel. '99 (first UMTS release); 410 million subscriber;161 countries; approx. 60% of world-market

    1997 Phase 2+: Annual Release `96

    DCS1800 / PCS1900 GSM1800 / GSM1900

    Dual-band devices

    GSM: practical world standard (109 countries/regions; 28 % market share)

    1998 Phase 2+: Annual Release `97: GPRS, CAMEL,....

    First GSM-R networks

    World-wide accessibility using dual mode GSM/IRIDIUM

    35 % of world market

    1999 Phase 2+: Annual Release 98

    250 M. subscriber, 130 countries

    2000 Phase 2+: Annual Release 99: AMR, VHE,... identical to UMTS Rel. 99

    60% of world market; 410 M. subscriber, 161 countries

    GSM Milestones

    Fig. 12

    18

    Introduction Siemens

  • Siemens Introduction

    The GSM Technical Guideline

    Objective (1982): Development of a unified, international standard for mobilecommunications. Guideline from the start:2 x 25 MHz frequency bands at 900 MHzare reserved by the CEPT for mobile communications in Europe in 1978. 1982:Roaming; the user can change location, keep the connection and be reached in theentire range of a PLMN and in the entire GSM range (International Roaming) as longas roaming agreements have been made. One user - one number; the subscribercan be reached at a single personal number in the entire GSM range, i.e. in variouscountries and PLMNs.

    Late objectives: Maximum flexibility to other services, e.g. ISDN (Integrated ServicesDigital Network; 1984) Vast service offers, i.e. technical possibilities of the PSTN/ ISDN and special features of mobile communications Safeguarding frominterception and subscriber license fraud; data protection.

    The GSM Recommendations

    The GSM Standard is a consistent and open standard for cellular mobilecommunication systems established by the ETSI. All aspects of the realization of theGSM Standard have been established in now more than 150 recommendations(technical specifications). Subsystems, network components, interfaces, signaling,tests and maintenance aspects etc. are described. This allows a harmoniousinteraction of all elements of a mobile communication network designated as PLMN(Public Land Mobile Network). At the same time the Recommendations are flexibleenough for the different realizations of various vendors. The Recommendations areorganized into 12 series according to different aspects. This structure reflects thestructure of the PLMN system and its interfaces.

    19

    Introduction Siemens

  • Introduction Siemens

    GSM Recommendation

    MSC

    PSTN

    ISDN BSS MS

    Series 01: General

    Series 02: Service Aspects

    Series 03: Network Aspects

    Register

    Series 04:

    MS/BS Interface

    & Protocols

    Series 05:

    Um Radio

    Transmission

    Series 06:

    Speech Coding

    Series 067:

    Terminal

    Adaptors for MS

    Series 08:

    MSC-BSS Interface

    Series 09:

    Network Interworking

    Series 10:

    Service Interworking

    Series 11: Equipment & Type Approval Specifications

    Series 12: Operation & Maintenance

    12 Series; each max. 100 Rec.:e.g. GSM Rec. 08.07

    Fig. 13

    20

  • Siemens Introduction

    The Evolutionary Concept

    The GSM Standard consists of multiple of recommendations. They are organized byvarious aspects and already comprised 5230 pages when the first phase wasadopted in 1990. It was originally planned to comprise every specification in the GSMStandard (with the exception of half rate speech") from the start, i.e. when thestandard was adopted. In 1988 it was recognized that not all of the planned servicescould be specified in the expected time frame. This led to the important decision toleave the GSM Standard incomplete and to leave space for further modifications andtechnical developments. This evolutionary concept secures for GSM the possibility ofpermanently adapting to the requirements of the market and thus ensures of notbecoming old-fashioned within a couple of years owing to the extremely fastdevelopment in this market sector.

    GSM Phase 1

    The Phase 1 standardization was closed in 1990 for GSM900 and in 1991 forGSM1800. The implementation of GSM systems Phase 1 comprises all of the mostimportant prerequisites for digital information transmission. Speech transmission is ofthe greatest importance here. Data transmission is also defined by data transmissionrates of 0.3 to 9.6 kbit/s. GSM Phase 1 comprises only a few supplementary servicessuch as call forwarding and barring.

    GSM Phase 2

    The Phase 2 standardization work started shortly after completion of Phase 1 andwas closed in 1995. In Phase 2 Supplementary Services comparable to ISDN(Integrated Services Digital Network) were included in the standard. Technicalimprovements have been specified, e.g. the Half Rate Speech. In Phase 2, thedecision on future downward-compatibility with older versions is of high importance.

    GSM Phase 2+

    GSM Phase 2+ refers to a smooth transition in contrast to Phase 2. A new completeupdate of the GSM Standard is not planned. Individual topics are discussedseparately and the update is added to the GSM standard in Annual Releases. Maintopics are new Supplementary Services as the ASCI services (Advanced SpeechCall Items). Furthermore, the IN feature Customized Applications for Mobile networkEnhanced Logic CAMEL and Virtual Home Environment VHE are very important.Especially the introduction of features to achieve higher data rates, i.e. HSCSD (HighSpeed Circuit Switched Data), GPRS (General Packet Radio Service) and EDGE(Enhanced Data rates for the GSM Evolution) has received much attention. GSMPhase 2+ thus paves the way to 3G (UMTS).

    21

    Introduction Siemens

  • Introduction Siemens

    Phase 1Phase 2

    Phase 1

    Phase 2+

    Phase 2

    Phase 1

    Services

    Year1991 1995 1997

    Full Rate Speech (FR),

    Standard services

    Data: max. 9.6 kbit/s

    New services e.g.

    MTPy, CUG, AoC;

    Half Rate Speech (HR)

    New services e.g.

    ASCI, SOR, UUS

    EFR;

    IN: CAMEL

    Data: HSCSD, GPRS,

    EDGE (> 100 kbit/s)

    Annual Releases !

    GSM: Evolutionary Concept

    Downward compatibility

    MTPy:

    CUG:

    AoC:

    ASCI:

    SOR:

    UUS:

    EFR:

    IN:

    CAMEL:

    HSCSD:

    GPRS:

    EDGE:

    Multiparty Service

    Closed User Group

    Advice of Charge

    Advanced Speech Call Items

    Support of Optimal Routing

    User to User Signalling

    Enhanced Full Rate Speech

    Intelligent Network

    Customized Applications for

    Mobile network Enhanced Logic

    High Speed Circuit Switched Data

    General Packet Radio Service

    Enhanced Data Rates for the GSM

    Evolution

    Fig. 14

    22

  • Siemens Introduction

    Adaptations of the GSM Standard

    The GSM adaptations GSM900, GSM1800, GSM1900, GSM-R and GSM400 differ inthe frequency ranges used and the resulting different technical implementations.

    GSM900 (GSM, E-GSM)

    Originally 2 x 25 MHz in the frequency range around 900 MHz (890 - 915; 935 - 960MHz) were provided for mobile communication applications. In an extension of thisrange, called E-GSM (Extended GSM) these ranges will be increased to 2 x 35 MHz(880 - 915; 925 - 960 MHz) on a national level when further operation licenses expire.

    GSM1800 (DCS1800)

    As an adaptation of the GSM900 Standard the DCS1800 Standard (Digital CellularSystem) was introduced in 1991. The DCS1800 was a British initiative with theintention of opening mobile communications to all sections of population as a massmarket, especially in urban areas. The GSM1800 has 2 x 75 MHz in the frequencyrange around 1800 MHz (1710 - 1785; 1805 - 1880 MHz). In 1997 the designationDCS1800 was changed to GSM1800 in order to clarify the common standard.

    GSM1900 (PCS1900)

    The PCS1900 Standard (Public Cellular System) is the American branch of the GSMStandard since 1995/96 in the frequency range around 1900 MHz. The frequencyrange available between 1850 - 1910; 1930 - 1990 MHz in the USA was split up in1995 and auctioned off to different net-work operators. In 1997 the PCS1900 wasrenamed GSM1900 in order to clarify the common standard.

    GSM-R (Railway)

    For mobile communication of railway operators 2 x 4 MHz in the frequency range of876 880 MHz & 921 925 MHz have been reserved.

    GSM400

    With Rel. '99 the frequency ranges between 450.4 457.6 MHz & 460.4 467.6 MHzrespectively the ranges (of former 1G systems) between 478.8 486 MHz & 488.8 496 MHz are foreseen for GSM400. The GSM400 frequency range enables largearea cells for rural environment.

    23

    Introduction Siemens

  • Introduction Siemens

    876 880

    890

    GSM

    900

    915 921 925

    935

    960 1710 1785 1805 1850

    1880

    1910 1930 1990[MHz] [MHz]

    GSM

    900

    E-GSM E-GSM

    GSM

    1800

    GSM

    1800

    GSM

    1900

    GSM-R GSM - Adaptations

    GSM

    1900

    Frequency Range[MHZ]

    Useable HFchannels

    Application Area

    GSM400 450.4 457.6 / 460.4 467.6

    478.8 486 / 488.8 - 496

    35 rural environment

    GSM900E-GSM

    890 - 915 / 935 - 960880 - 915 / 925 - 960

    124174

    Worldwide exceptAmerica

    GSM1800 1710 - 1785 / 1805 - 1880 374 Worldwide exceptAmerica

    GSM1900 1850 - 1910 /1930 - 1990 299 America

    GSM-R 876 - 880 / 921 - 925 19 Railway systems

    Fig. 15

    24

  • Siemens Introduction

    The GSM-PLMN

    In the GSM System there must be a distinction between network operator, provider oftelecommunication services, supplier of terminal equipment and manufacturer ofnetwork components. Especially the sale of telecommunication services and terminalequipment differs from the conventional fixed network and mobile communicationnetwork of the first generation, in which state-owned network operators, serviceproviders and equipment suppliers usually form a monopoly. In GSM the actualnetwork operator often transfers services to private providers who supply theservices to the mobile subscribers under different conditions. With the wide range ofproducts there is also great competition in the field of mobile equipment as well as ofmobile communication network components which should force further technicaldevelopment and keep the prices down.

    PLMN - Public Land Mobile Network

    A PLMN is a terrestrial mobile communication network set up and run by public andprivate operators. It is used to provide public mobile communication services.

    General Objectives of a GSM-PLMN (with respect to service aspects):

    a) Provision of a wide range of speech and non-speech services andcompatibility to those services offered in fixed telecommunication networkssuch as PSTN, ISDN and PDN;

    b) Additional provision of specific services for mobile access environment;

    c) Compatible access for mobile subscribers in all countries where the GSMSystem is operated;

    d) Provision of roaming (roaming agreement) and automatic updating;

    e) Location registration of mobile subscribers in these countries;

    f) Provision of sufficient quality of service;

    g) Provision of services with a wide range of mobile stations, e.g. permanently in-stalled in vehicles, so-called portables and hand stations (mobile phones).

    General Objectives of a GSM-PLMN (with respect to performance aspects):

    a) Guarantee of a high spectrum efficiency;

    b) Provision of a system concept which will lead to attractive costs regardinginfra-structure and mobile equipment

    25

    Introduction Siemens

  • Introduction Siemens

    GSM-PLMN(Public Land Mobile Network)

    Example:

    Germany

    Competition concept:different network operators,

    providers and manufacturers

    D1Telekom

    D2Mannesmann

    Eplus

    E2Viag Intercom

    Fig. 16

    26

  • Introduction Siemens

    3 Current Situation, Market & Trends

    0,01

    0,1

    1

    10

    100

    1000

    1980

    1982

    1984

    1986

    1988

    1990

    1992

    1994

    1996

    1998

    2000

    Introduction

    Current Situation,

    Market & Trends

    Fig. 17

    27

  • Siemens Introduction

    Overview: Systems/Standards

    At the time there is a wide spectrum of mobile communication systems of the first andsecond generation along with the GSM Standard and its adaptations. Importantexamples include:

    Paging Systems

    Cordless Telephone

    Wireless Local Loop

    Private Mobile Radio

    Cellular Mobile Systems

    Mobile Satellite Systems

    These different systems differ in:

    Target groups

    Services offered

    Prices

    Coverage

    Degree of mobility

    Technical principles / realization

    28

    Introduction Siemens

  • Introduction Siemens

    analogue cordless telephone systems

    e.g. CT1, CT1+

    digitalpaging systems

    e.g. ERMES

    analoguepaging systems

    e.g. Citycall

    Cordless

    telephone booth

    digital cordless telephone systems

    e.g. DECT, PACS, PHP

    analoguePrivate Mobile Radio

    PMR

    Wireless Local Loop

    WLL

    digitalPMR

    e.g. TETRA

    digital cellular systems

    e.g. GSM, D-AMPS,

    PDC, IS-95

    digital satellite systemse.g. IRIDIUM, ICO,

    Globalstar

    analoguecellular systems

    e.g. C450, NMT, AMPS

    analoguesatellite systemse.g. INMARSAT

    Current

    Mobile

    Communication

    Systems

    Differences: target groups

    services offered

    prices

    coverage

    degree of mobility

    transmission technique

    ...

    1G 2G

    Fig. 18

    29

  • Siemens Introduction

    1G Systems

    C450: closed 12/2000

    TACS (Total Access Communications System): closed 2001.

    NMT (Nordic Mobile Telephone): closed 2001.

    AMPS (Advanced Mobile Phone Service): The AMPS system was introduced in 1979in the USA. The system, operated in the frequency range of 800 MHz, was the mostsuccessful mobile radio system in the world until 1997. It still has an increasingnumber of subscribers, because of its large coverage in the USA. 12/2000, more than75 million AMPS subscribers were registered.

    2G Systems

    GSM (Global System for Mobile Communications): The GSM Standard wasadopted as the first digital mobile communication standard, as planned since theearly 80s. Commercial operation started in 1992. This led to the world-wide use ofGSM net-works, which were originally planned for the European system, in more than120 countries and regions. GSM uses a hybrid solution of FDMA and TDMA as anaccess technique. GSM used currently 900 / 1800 /1900 frequency ranges.

    D-AMPS (Digital Advanced Mobile Phone System): The D-AMPS was conceivedas a supplementary system to the successful analogue AMPS in the USA andCanada. The commercial start was 1991/92. D-AMPS as IS-136 standard is basedon a combined FDMA/TDMA access technique. It shares the 800 MHz range withAMPS (824 - 849; 869 - 894 MHz). It expanded to the 1900 MHz range in 1995.Multimode / multiband equipment is used for AMPS/D-AMPS.

    PDC (Personal Digital Cellular): With the influence of D-AMPS, PDC (originallycalled JDC - Japanese Digital Cellular) was standardized for the Japanese market.The commercial start was 1993/94. A combined FDMA/TDMA procedure, similarly tothe D-AMPS, is used as an access procedure. Mobile stations transmit at the higherfrequency with PDC, in contrast to all other systems. Frequencies around 900 MHz

    (810 - 826; 940 - 956 MHz) & 1500 MHz (1429 - 1453; 1477 - 1501 MHz) are used.

    IS-95 CDMA IS-95 CDMA was developed in the early 90s based on CDMA spreadspectrum digital technology and was declared IS-95 standard in 1993. Thecommercial start was 1995/96. IS-95 CDMA networks are emerging world-wide withemphasis on North America and Eastern Asia. Frequencies in the 800 MHz and 1900MHz range are used world-wide, and also in the 1700 MHz range in Korea.

    30

    Introduction Siemens

  • Introduction Siemens

    Cellular Systems

    First generation:C450

    NMT - Nordic Mobile Telephone

    TACS - Total Access Communications SystemAMPS - Advanced Mobile Phone System

    Second generation:

    GSM D-AMPS PDC IS-95

    Start 1992 1991/92 1993/94 1995

    Coverage worldwide especiallyUSA, Canada

    Japan especially USA,Canada, EasternAsia

    Frequency

    ranges [MHz]

    900 / 1800 /1900 (America)

    800 / 1900 900 / 1500 800 / 1700 (Korea) /1900

    Multiple

    Access

    TDMA / FDMA TDMA / FDMA TDMA / FDMA CDMA

    Speech [kbit/s] 13 / 5.6 7.95 6.7 9.4 / 13

    Data (max.)

    [kbit/s]

    9.6(n14.4; n = 1...8)

    4.8 4.8 9.6 / 14.4

    Subscribers

    (02/2001)

    ~ 410 million ~ 35 million + 75 million (AMPS)

    ~ 55 million ~ 85 million

    Fig. 19

    31

  • Siemens Introduction

    Mobile Satellite Systems MSS

    Large areas of the earth's surface can not be covered by fixed or mobile networks.Mobile Satellite Systems MSS are offered for supplying scarcely populated regionsand areas with weak infrastructure. Satellite supported mobile communicationsystems are useful for high-sea ship transport, for catastrophe regions, and foremergency supply.

    Satellite systems can be distinguished with respect to their orbits:

    GEostationary Orbit - GEO, with approx. 36,000 km altitude;

    High Elliptic Orbit - HEO;

    Medium Earth Orbital - MEO, from 10,000 - 20,000 km;

    Low Earth Orbital - LEO, from 700 - 1,500 km.

    1G MSS

    MARISAT (Maritime Satellite): MARISAT went into operation in 1976 as the firstmobile satellite system, initiated by the USA.

    INMARSAT (International Maritime Satellite Organization): INMARSAT is taking adominant role in 1G MSS. Founded in 1979, it is used by more than 100 membershipcountries. The four INMARSAT (operation) satellites are in a geostationary orbit(about 36,000 km altitude). With the exception of a the pole caps, a globaltransmission to the world is achievable. Digital transmission is via INMARSATsatellites since 1995., i.e. INMARSAT has turned over to a 2G MSS system

    2G MSS

    Digital information transmission and a larger number of satellites in lower orbits (LEOand MEO satellites) allow considerably higher capacity. Several services similar tothose of GSM should be possible. A problem of the 2G systems is the comparablehigh price and fast extension of 2G terrestrial networks

    Iridium (closed 2000)

    Globalstar

    ICO

    Ellipso

    ORBCOMM

    Teledesic

    Skybridge

    32

    Introduction Siemens

  • Introduction Siemens

    Supply to/ in case of:

    - inaccessible, underpopulated areas

    - poor infrastructure- high seas- catastrophe areas

    - failure of other supplies

    Supply to/ in case of:Supply to/ in case of:

    - inaccessible, underpopulated areas- poor infrastructure

    - high seas- catastrophe areas- failure of other supplies

    GEOGEostationary Orbit

    10,000- 20,000 km

    700- 1,500 km

    MEO MediumEarth Orbit

    approx.36,000 km

    LEOLow Earth Orbit

    Mobile Satellite Systems MSS

    HEOHigh Elliptic

    Orbit

    1G:

    MARISAT (USA) since 1976

    INMARSAT (International Maritime

    Satellite Organisation): since 1979; > 80 member countries 4 GEO satellites; global access

    2G: Iridium, ICO, Globalstar

    private MSS operator speech- & low data rate services

    Earth

    Fig. 20

    33

  • Siemens Introduction

    The Mobile Market: Subscriber Trends 1980 - 2000

    Before the introduction of first generation of cellular mobile communication systems,the mobile communication market was unimportant. One-cell systems had only a fewthousand subscribers and slow annual growth rates in Europe, North America, andJapan. Until the introduction of the first cellular systems in 1979 (AMPS: USA, NTT-MTS: Japan) fewer than a million subscribers were registered worldwide.

    The introduction of the first generation (analog) cellular mobile communicationsystems led to a quantum leap on the mobile communication market. There wereannual growth rates of 10 to more than 50 %. In the early nineties, there were morethan a million subscribers registered in both the USA (AMPS) and Great Britain(TACS) each. Several hundreds of thousands of subscribers were registered in othercountries with systems such as NMT, C450, NTT-MTS. The number of worldwidesub-scribers exceeded 10 million in 1990. Simultaneously the limits of analoguecellular systems were apparent in many countries owing to capacity problems,especially in densely populated urban regions.

    The introduction of GSM as the first mobile communication standard of the second(digital) generation allowed an improved transmission quality, a larger offer ofservice, various technical / organizational improvements, and a considerably moreefficient use of radio interface resources. A significant increase of capacity and thusfurther growth of the mobile communication market became possible. Already shortlyafter the start of GSM in 1992, subscriber numbers exceeded the million mark inmany countries. Other digital systems such as IS-95 followed. A development to agenuine mass market has been evident since the introduction of the secondgeneration of mobile communications.

    34

    Introduction Siemens

  • Introduction Siemens

    0,01

    0,1

    1

    10

    100

    1000

    Su

    bs

    cri

    be

    r [M

    .]

    1980

    1982

    1984

    1986

    1988

    1990

    1992

    1994

    1996

    1998

    2000

    Year

    Germany

    World

    Subscriber trends:

    1980 - 2000

    1G

    IntroductionSingle cell

    systems

    2G

    Introduction

    Fig. 21

    35

  • Siemens Introduction

    Trends & Outlook

    The mobile communication market will expand greatly in the future as well. Incontrast to the fixed network sector, which has developed slowly in the past decadesand has only recently become more dynamic, many predict unhindered growth for themobile communication sector beyond the year 2000. Only the growth of the Internetis expected to exceed the growth of the mobile communication sector. It is generallyexpected that the number of the mobile communication subscribers will rapidlyapproach that of the fixed subscribers, and that in regions with a poorly set up infra-structure, the number of mobile communication subscribers will clearly exceed that offixed subscribers within the foreseeable future.

    Almost three billion mobile communication subscribers world-wide are expected by2015. This growth is apparent in the currently developing countries and newlyindustrialized countries of the Asian / Pacific region. A 50 % share of the worldwidemobile communication market is expected for the Asian / Pacific region by 2015; forindustrial nations in North America and Europe (EU15), a share of only about 7 % -11 % is expected.

    0'

    500'

    1000'

    1500'

    2000'

    2500'

    1995 2000 2005 2010 2015

    RoW

    As ia / P ac ific

    North A m eric a

    EU 15

    UMTS Forum

    Report #1

    Trends & Outlook

    Su

    bscri

    ber

    [M.]

    Year

    Fig. 22

    36

    Introduction Siemens

  • Siemens Introduction

    Mobile Trends

    The mobile radio systems of the second generation have been optimized for speechtransmission. Data transmission is possible, but has previously been consideredsecondary. Taking the increasing mobility in the professional world (work outside theoffice, telework) into consideration, the need for mobile transmission of data is in-creasing. Comparatively user-unfriendly terminals (adapter solution) and relativelylow data transmission rates are problems for data transmission of the secondgeneration of mobile communications. The data rates for GSM are between 0.3 - 9.6kbit/s, the transmission rates of other cellular standards are comparable or less. Thefirst mobile satellite systems of the second generation also have only low datatransmission rates (Iridium max. 2.4 kbit/s, Globalstar max. 9.6 kbit/s). These ratesare considerably lower than those of ISDN (64 kbit/s).

    A large variety of demands are being placed on future mobile communications. Alongwith improved world-wide service, user friendliness and cost reduction, mobile PCInternet connection with a high data transmission rate is required.

    Many of these demands are taken into account in GSM Phase 2+.

    In this way bearer services were standardized with transmission rates in order to in-crease data transmission rates as well as to realize mobile computing and accessto the Internet. Data transmission rates can be adapted to the transmission rates ofISDN and can be increased significantly further (up to more than 100 kit/s) by meansof these bearer services. User friendly equipment and cost-reduced features are alsoplanned, such as improvements in speech quality and world-wide availability bymeans of satellite roaming. Furthermore flexible services adaptable to customer re-quests and intelligent network services are planned.

    37

    Introduction Siemens

  • Introduction Siemens

    Trend:

    Voice Data

    Mobile Trends

    Source:

    UMTS Forum

    0

    20

    40

    60

    80

    100

    Tra

    ffic

    [%

    ]

    1996 2001 2005 2007

    Year

    Voice

    DataRequirements: high data rates user-friendliness

    improved service offering

    cost reduction

    worldwide accessibility

    GSM Phase 2+ data rates > 100 kbit/s mobile computing, Internet

    new, integrating ME

    new flexible services + IN

    satellite roaming

    & much more

    Fig. 23

    38

  • Siemens Introduction

    Mobile Forecast (Europe)

    10 % of the traffic is expected to be on the data transport radio interface already in2001, 30 % in 2005.

    If further capacities and higher data transmission rates are achieved, there are hardlyany limits to a further growth of the mobile communication market even after thenumber of subscribers reaches saturation.

    The market share of speech transmission is as of 2007 expected to be less than 50% in the entire volume of traffic.

    An enormous change in the proportion of speech transmission to data transmissionhas thus been predicted in the use of mobile communications in the first decade ofthe 21st century.

    It will be expected

    change from speech to data transmission

    high data rate multimedia applications.

    Predictions assume a minor but slowly increasing share of multimedia users inEuropean mobile communications after the implementation of GSM Phase 2+features, HSCSD and GPRS (as of 2000).

    This is also the limit of GSM. Although the performance capacity of GSM Phase 2+far exceeds the original expectations for the second generation of mobilecommunications, neither the frequency ranges available nor the narrow-bandfrequency use in GSM suffice for the predicted increases and demands regardingdata transmission, especially multimedia use.

    The third generation of mobile communications with GSM's successor, the UMTS(Universal Mobile Telecommunications System) is to deal with these applications anddemands as of 2002.

    A considerable increase in multimedia use is expected with a wide-range expansionof UMTS as of 2005. Predictions of the UMTS forum assume that of the approx. 260million European mobile communication subscribers in 2010, approx. 90 million couldbe multimedia users, while the rest of the users use only speech and low data rateservices. Multimedia users will produce more than 50 % of the entire traffic rate.

    39

    Introduction Siemens

  • Introduction Siemens

    Mobile subscriber

    (total)

    Mobile subscriber

    all applications from

    voice to Multimedia

    Mobile subscriber

    Speech only/

    low data rates

    Mobile communication

    forecast (Europa)

    mobile Multi Media:

    Start with GSM Ph2+

    Breakthrough:

    3G (UMTS)Source: UMTS-Forum

    0'

    50'

    100'

    150'

    200'

    250'

    300'

    1995 2000 2005 2010

    Year

    Su

    bs

    cri

    ber

    [M.]

    Fig. 24

    40

  • Siemens Introduction

    The Third Generation (3G)

    There are at the time many mobile communication standards of both the second and(still) first generations. Cellular mobile networks of the most different standardscomplement one another or compete with private mobile radio systems, cordlessstandards, paging systems and satellite systems, etc. Every one of these standardshas specific features, advantages and disadvantages, applications and user circles.Many of these systems exist only on a national level and/or are incompatible. To acertain extent this scenario reassembles on a world-wide level the situation of thecellular systems in Europe before the introduction of GSM.

    IMT-2000 (International Mobile Telecommunications 2000)

    The third generation of mobile communications represents a world-wide system ofcompatible standards, in which the most various current and future demands ontelecommunications have to be dealt with. The main task is to provide services to thecustomer, independently of his location and the specific available infrastructure.Smooth mobility should be guaranteed over all operator-dependent, national andgeographic borders at any location.

    The demands on the third generation mobile communication systems have beendiscussed since the early 90s under the term FPLMTS (Future Public Land MobileTele-communications Systems). The term FPLMTS was changed into a term easierto pronounce, IMT-2000, in the mid 90s for countries in which English is not a nativelanguage. IMT stands for International Mobile Telecommunications 2000 indicatesboth the approximate date of introduction and the frequency range.

    The International Telecommunications Union - ITU - is responsible for the IMT-2000specification. IMT-2000 is planned as the world-wide guideline of all standards of thethird generation of mobile communications. All of the "regional" standardization unitsfor developing standards must fulfil the ITU stipulations for IMT-2000. This ensures acompatibility of the standards to be specified without hindering innovative individualdevelopment and competition.

    Many regional standardization committees create their own standards under the IMT2000 "roof". Nevertheless, UMTS (Universal Mobile Telecommunication System) asGSM successor system is expected to dominate the 3G market

    41

    Introduction Siemens

  • Introduction Siemens

    e.g. UMTS, cdma2000, UWC-136

    2G(digital)

    Paging Systems

    e.g. ERMES

    Cordless Telephonee.g. DECT, PACS, PHS

    WirelessLocal Loops

    WLL

    PMRe.g. TETRA

    Cellular systems

    e.g. GSM, D-AMPS,IS-95, PDC

    MSS

    e.g. IRIDIUM, ICO, Globalstar

    1G(analog)

    Cordless Telephonee.g. CT1, 1+

    Paging Systems,

    e.g. City Call

    wirelessTelephone cell

    Private Mobile RadioPMR

    Cellular systems

    e.g. C450, NMT, AMPS

    MSS

    e.g. INMARSAT

    3G

    1 family of

    standards

    for all

    applications

    countries

    different, incompatible standards for

    different applications, countries & regions

    IMT-2000

    Fig. 25

    42

  • Siemens Introduction

    UMTS - Universal Mobile Telecommunications System

    The ETSI (European Telecommunication Standards Institute) has specified UMTS asthe successor of GSM; a forum call Third Generation Partnership Project 3GPP, co-operating with the most important standardization organizations of the world isresponsible since 12/98. UMTS will fulfil the requirements for IMT-2000.

    With UMTS world-wide multimedia access is possible at any time to all ranges whichare currently operated by various mobile communication systems of the first andsecond generations.

    Data rates of 8 kbit/s to 2 Mbit/s are to be supported. UMTS will support zone 1 3 ofthe four zones of the IMT-2000 concept:

    Zone 1 Indoor: for offices, private households,...; for low speed (stationary / up to10 km/h) max. data rates up to 2 Mbit/s are theoretically possible.

    Zone 2 Urban: for city, shopping malls, railway stations, subways, airport halls forlow speed (stationary / up to 10 km/h) max. data rates up to 2 Mbit/s aretheoretically possible.

    Zone 3 Suburban/Rural: For wide range mobility (car, train) with higher / highspeeds (up to 120 / 500 km/h), 384 kbit/s 144 kbit/s should be possible. (Remark:for UMTS only the lower speed value is currently planed)

    Zone 4 Global: For rural, thinly populated areas with low user densities. All speedsfrom stationary (individual buildings, measuring stations), to intermediate speeds(car, train, ship), to 1000 km/h (airplanes). Mobile satellite systems (e.g.INMARSAT: Horizons) which ensure up to 144 kbit/s are planned for servicing.

    For IMT-2000 the frequency ranges from 1885 - 2025 MHz and from 2110 - 2200MHz should be reserved (requested by ITU).

    UMTS uses in Europe the frequency ranges of 1900 - 1980 MHz, 2010 - 2025 MHzand 2110 - 2170 MHz.

    The frequency ranges of 1980 - 2010 MHz and 2170 - 2200 MHz are reserved for 3GMSS.

    43

    Introduction Siemens

  • Introduction Siemens

    Zone 4: Global

    Zone 3:

    Suburban / Rural

    Zone 2:Urban Zone 1:

    IndoorPicoCellMicro

    CellMacro

    CellMSS

    max.

    data rate144 kbit/s 384 kbit/s 2048 kbit/s144 kbit/s

    UMTS - Universal Mobile Telecommunications System

    1 8 5 0 1 9 0 0 1 9 5 0 2 0 0 0 2 0 5 0 2 1 0 0 2 1 5 0 2 2 0 0 2 2 5 0

    cellular MSS cellular MSS

    1885

    2010

    2110

    1980

    2025

    2170

    2200

    Frequency range [MHz]

    Fig. 26

    44

  • Chapter 2

    Transmission Principles

  • Transmission Principles

    Transmission Principles

    Contents

    2GSM Network Structure 1 14 Duplex Transmission & Multiple Access 2 21 GSM - Fixed Network Transmission 325GSM Air Interface 4

  • Transmission Principles Siemens

    1 GSM Network Structure

    Transmission Principles

    GSM Network Structure

    Fig. 1

    2

  • GSM: The Network Structure

    The international GSM service area covers all countries in which there is a GSMnetwork.

    Networks provisioned by an operator on a national level for public mobilecommunication are called Public Land Mobile Networks PLMN. PLMNs builttogether with public fixed networks, i.e. "conventional" PSTN (Public SwitchedTelephone Network) or ISDN (Integrated Services Digital Network) networks thetelecommunication infrastructure of a country.

    A Public Land Mobile Network is divided into mobile and fixed network components.They are connected via air interfaces.

    Fixed Network Components of the PLMN

    The fixed network components of a GSM-PLMN consist of:

    Base Station Subsystem BSS: The BSS is the fixed network part of the PLMNradio access (Radio SubSystem RSS). It realizes the radio transmission via theradio interface. Several fixed radio station, so-called Base Stations BS are co-ordinated by one control unit.

    Network Switching Subsystem NSS: The NSS forms the interface between theradio subsystem and the public fixed networks (PSTN, ISDN, PDN). It executes allsignaling functions for setting up connections from and to mobile subscribers. It issimilar to the exchanges of fixed network communication systems, but itfurthermore fulfils important mobile communication specific functions, e.g. keepingtrack of the users / mobile stations location.

    Mobile components of the PLMN

    The Mobile Stations MSs are regarded as mobile part of the PLMN. The air or radiointerface represents the connection between the MS and the PLMN fixed networkcomponents BSS and NSS. The organization of the radio interface is decisive foradvantages and disadvantages of different mobile systems.

    3

    Transmission Principles Siemens

  • Transmission Principles Siemens

    Mobile

    terminal device

    BSSBase Station

    Subsystem

    NSSNetwork Switching

    Subsystem

    control/switching of

    mobile services

    BSSBase Station

    Subsystem

    BSSBase Station

    Subsystem

    PLMNPublic Land Mobile Network

    PSTNPublic Switched

    Telephone Network

    ISDNIntegrated Services

    Digital Network

    PDNPublic Data

    Network

    MSMobile

    Station

    Mobile

    components

    Fixed network

    components

    UmAir Interface

    Fixed

    network

    GSM Network Structure: Concept

    Fig. 2

    4

  • Mobile Components

    Mobile components are the Mobile Stations MS which transmit the users speech anddata to the PLMN. The Mobile Station MS consist of:

    ME: Mobile Equipment,

    SIM: Subscriber Identification Module,

    The MS is not necessarily the termination point for the users data transmission. ATerminal Equipment TE, e.g. laptop, fax machine,... can be connected to the MS forfinal data handling.

    The Mobile Station MS

    An important difference between fixed network communications and mobilecommunications is the separation of equipment and subscriber identity. It is possiblefor the mobile subscriber to use various mobile terminal equipment with a personalidentity by means of the SIM card, which includes his subscriber identity. The mobilestation is defined as: MS = ME + SIM.

    The SIM card is allocated and activated by the provider upon completion of thecontract. It is realized by means of a chip which contains a variety of permanent andtemporary information for the subscriber (e.g. personal telephone register) and abouthim/her. Along with the personal (secret) ID numbers (IMSI - International MobileSubscriber Identity, TMSI - Temporary Mobile Subscriber Identity) these storedinformation are for example algorithms and keys for ciphering the transmission.

    The PIN (Personal Identity Number) is important for the subscriber; it must beentered by the mobile subscriber before the start of the conversation in order toprevent fraud by unauthorized intruders. As a rule, calls cannot be made without aSIM card in the ME and without the PIN being entered. Emergency calls are anexception.

    5

    Transmission Principles Siemens

  • Transmission Principles Siemens

    SIMSubscriber Identification Module

    MS = ME + SIM

    Mobile Components

    SIM card: the heart of MS

    Different equipments, one SIM (one bill) Security: PIN (exception: emergency call) Chip with subscriber identification,

    security algorithms,

    personal phone book,...

    Fig. 3

    6

  • The Cellular Network

    The breakthrough in mobile communications with regards to subscriber numbers andcapacity was made possible by the introduction of the cellular radio system. Thecellular communication system was tested in various countries during the 1970s.

    Cellular networks of the first generation were introduced, e.g.:

    1979 in the USA: AMPS (Advanced Mobile Phone Service)

    1981 in Scandinavia: NMT (Nordic Mobile Telephone)

    1985 in Germany: C-450 (Siemens)

    1985 in Great Britain: TACS (Total Access Communications System)

    The successive digital systems of the second generation, and therefore GSMsystems, are structured as cellular communication systems in the same way as theanalogue systems.

    Principle of the Cellular Communication System

    PLMNs operating on a national level are divided by location into servicing areas, so-called cells, in which a Base Transceiver Station BTS supplies the mobile subscribersof the area concerned. The cells represent the smallest service area in the PLMNnetwork.

    A variety of cells ensures service of the total PLMN service area. The cells aretheoretically arranged in a so-called honeycomb pattern. Adaptations to thepopulation/ traffic density and the topography of the service area lead to a moreirregular pattern.

    The service areas of the individual cells partially overlap. In order to avoidinterference of different subscribers in surrounding cells the cell structure isorganized according to the principle of cellular systems, frequency re-use. Thenarrow available frequency range is divided into individual frequencies (channels).Only some of these channels are used in a certain cell, the remaining channels areused in the adjacent cells. The same frequency is used again in cells which aresufficiently far apart from each other to avoid interchannel interference. This meansthat any area can be covered and thus an enormous increase in network capacitycan be achieved with a small supply of channel frequencies.

    7

    Transmission Principles Siemens

  • Transmission Principles Siemens

    The Cellular

    Network

    Principle: Many cells (BTS)

    Full coverage

    Partial overlap of cells

    Distribution of frequency resources

    Only a few frequencies per cell

    Frequency re-use

    Solution:

    cell,

    radio cell

    r = cell radius(cell parameter)

    Principle:

    ~ 4 r

    channels

    u, v, w

    channels

    x,y,z

    r

    channels

    x,y,zco-channel interference zone

    = cluster area

    re-use distance

    for HF channel frequency

    re-use distancefor

    HF channel frequency

    Fig. 4

    8

  • Cluster

    A certain minimum distance must be maintained between cells using the samefrequencies in order to prevent interference or at least keep it to a bare minimum.This minimum distance, the so-called frequency re-use distance, depends on theconcrete network planning and corresponds to approximately 4 times the cell radius.On this principle, the available channels can be divided e.g. into 7 parts anddistributed over the PLMN area in such a way that each cell contains one of these 7sets of frequency channels. The minimum area in which the whole range of HFchannels is used is described as a cluster. Planning a concrete network implies thatthe population/traffic density, the topography of the area to be supplied, etc. must betaken into account. This network planning is an extremely difficult process; there isspecial network planning software for this purpose.

    Frequency re-use distance: avoid inter-channel interferences

    Cluster: smallest domain within which all frequency resource is used

    (GSM900: typ. 7/9 cells)

    Network planning: difficult

    The Cellular Network / Principles of Network Planning

    Fig. 5

    9

    Transmission Principles Siemens

  • The GSM Cell

    The higher the traffic density, the smaller the cell area since a limited number of HFchannels can only cope with a limited traffic volume. This can be carried out via areduction of the cell radius or by dividing the cells into sectors.

    Cell Size / Hierarchical Cellular Structures HCS

    The size and shape of the cell depend on:

    The range of the MS radio contact (MS output peak power); topography (e.g.mountains, buildings, vegetation etc) and climate play a role here.

    Traffic density

    The maximum radius of a cell broadcast channel is 35 km in the GSM900 system, 8km in the GSM1800 system. The possibility of setting up "extended range cells" witha radius of up to 100 km has been integrated into GSM Phase 2+ for GSM900systems. This should allow coverage of sparsely populated areas and especiallycoastal regions. The extended cell concept results in a reduced capacity.

    Transmit power is limited for higher traffic densities in order to achieve a high degreeof re-use of frequencies over smaller cells: The size of clusters is inverselyproportional to the capacity of the radio system.

    A Hierarchical Cell Concept (Rec. 05.22) is planned for towns, with an extremely highdensity of mobile subscribers.

    Macro-Cell: The "normal" cells are called Macro Cells. They have ranges fromapproximately one km to several (extended cell concept: 100 km).

    Micro Cell: Cells for the support of restricted areas with very high mobile userdensity, e.g. shopping malls, railway and subway stations, airport terminals. Theirradius ranges from some 100 meters to approximately 1 km.

    Pico Cell: Cells for the support of indoor applications, e.g. offices. Their rangeshould be several 10m.

    Velocity dependent Handover are necessary in the Hierarchical Cellular Structures.

    Cell Coverage

    Omni Cells: The BTS is equipped with omni-directional antennae and serves a360 angle.

    Sector Cells: The BTS supplies the cells with directional antennae. The cell shapeis a circular segment. Sectors of e.g. 180 or 120 are covered.

    10

    Transmission Principles Siemens

  • Transmission Principles Siemens

    Cell Size and Coverage

    Maximum cell size

    GSM90035 km

    (100 km)

    8 kmGSM1800

    Cell coverage

    360

    180180

    cell 1

    cell 2

    120120

    cell 1

    cell 2

    cell 3

    120

    omni cell

    180

    sector cells

    120

    sector cells

    (extended cell)

    Hierarchical Cellular Concept:

    Macro cells: min. 500 m

    Micro cells: some 100 m

    Pico cells: some 10 mspeed-dependent allocation

    Fig. 6

    11

  • Roaming / Location Registration / Handover

    Roaming

    A further innovation of the cellular system was so called Roaming. This means that asubscriber can move freely within the PLMN and remain reachable on a singlepersonal telephone number anywhere in this area. With GSM this concept of roamingcan be expanded to the international area (international roaming). A subscriberwhose home PLMN has a roaming agreement with other countries' GSM-PLMNs canalso be reached in these PLMNs (Visited PLMN - VPLMN) without dialing thecorresponding VPLMNs code; calls can also be made from that VPLMN. Aprerequisite is of course that subscribers authorization for international roaming.

    Location Registration / Location Update / Location Area

    The subscriber has to be located in the respective cellular network. A procedureknown as Location Registration or Location Update Procedure LUP carries outthis function. It is important that the subscriber's temporary location area is recorded /registered with this procedure when the subscriber's mobile station is switched onand checked in, to forward calls to him. The temporary Location Area LA is the areain which the MS can move freely without having to carry out a location update. As arule, the location area consists of a multiple cells and is configured by the operatoraccording to the traffic or population density.

    Handover

    In cellular networks, it is not necessary for the subscriber to have his call interruptedwhen changing from one cell's service area to the area of a surrounding cell, as longas the cell areas overlap. This overlapping should be guaranteed with good planning.If the MS can receive better supply from another cell than the one currently in useduring a call, the MS connection will be diverted to the relevant cell. This proceduredesigned for system quality maintenance ideally takes place without the user beingable to notice and is known as handover.

    12

    Transmission Principles Siemens

  • Transmission Principles Siemens

    Roaming, Location Update

    & Handover

    BS

    BS

    Location Update: Location Area: most precise location information

    stored in the network

    Location Registration: initial registration

    Location Update: update of registration

    MS

    Handover

    Fig. 7

    13

  • Transmission Principles Siemens

    2 Duplex Transmission & Multiple Access

    Transmission Principles

    Duplex Transmission

    & Multiple Access

    FDD TDD

    UL DL

    Duplex

    transmission

    Multiple

    Access

    FDMA

    TDMA CDMA

    Fig. 8

    14

  • Duplex Transmission and Multiplex Procedure

    In a cell for access to a network two different principles have to be co-ordinated: Theway of co-ordinating UL and DL, i.e. the Duplex Transmission, and the way ofenabling the simultaneous access of several user to the same Base Station, i.e. themultiple access principle.

    Duplex Transmission: FDD & TDD

    Modern cellular mobile radio systems of the first (1G) and second generation (2G)enable full duplex transmission. Simultaneous communication on both sides, i.e.(virtually) simultaneous transmission and reception is thus possible.

    The transmission directions are designated as Uplink UL (MS to BTS) and DownlinkDL (BTS to MS).

    There are two duplex transmission principles:

    Frequency Division Duplex FDD: Transmission and reception take place indifferent frequency ranges. The distance between the Uplink UL and Downlink DLfrequency range is designated as duplex distance.

    Time Division Duplex TDD: Transmission and reception take place in the samefrequency band. Uplink UL and Downlink DL transmission take place at differenttimes. There is fast switching between UL and DL transmission, so that the userhas the impression of simultaneous transmission and reception.

    receive

    transmit receive

    transmit

    transmit

    transmitreceive

    receiveMS

    BS

    UL ULDL DL

    time t

    T

    frequency f

    Duplex distance

    UL / DLseparated by

    frequency !

    Same

    frequency

    UL / DLseparated by

    time!

    FDDFrequency

    Division Duplex

    Uplink UL

    Downlink DL

    Base Station BS Mobile Station MS

    TDDTime

    Division

    Duplex

    Fig. 9

    15

    Transmission Principles Siemens

  • Multiplex Access: FDMA, TDMA and CDMA

    Several subscribers in one cell must be able to use the frequency range available formobile communications together. Thus there must be procedures for regulatingsimultaneous access of different subscribers without disturbances. There are threedifferent general procedures, partially in combination, which are used for co-ordinating the frequency resources:

    FDMA - Frequency Division Multiple Access

    TDMA - Time Division Multiple Access

    CDMA - Code Division Multiple Access

    FDMA - Frequency Division Multiple Access

    FDMA is a multiple access principle used widely in the first (analogue) generation 1Gof mobile communications. It is however also used in the second (digital) generation2G of mobile communications, usually in combination with TDMA and in the thirdgeneration 3G together with CDMA.

    The available frequency reserves are divided into channels of the same bandwidthfor FDMA. A certain frequency uplink and downlink is made available to an individualsubscriber. Simultaneous calls and information transmissions of various subscribersthus take place on different frequencies. The transmitter and receiver must have acommon knowledge about the channel frequencies to use.

    FDMAFrequency Division

    Multiple Access

    Multiplex Access

    TDMATime Division

    Multiple Access

    CDMACode Division

    Multiple Access

    Co-ordination

    of limited frequency resources

    for different subscribers

    Fig. 10

    16

    Transmission Principles Siemens

  • TDMA - Time Division Multiple Access

    The allocation of the available frequency range is made with respect to time forTDMA. A frequency band is not permanently available to one mobile station; it isused by several different mobile stations. Time is therefore split into individual timeslots. The individual mobile stations are assigned the frequency range for theduration of a TDMA time slot in a periodically exclusive manner.

    A certain number of subscribers can use a certain frequency range virtuallysimultaneously with TDMA. The message information of a subscriber is taken apartand transmitted piece by piece to the corresponding time slots. The informationcarrying HF transmission in an individual time slot designated as a "burst".

    CDMA - Code Division Multiple Access

    In CDMA systems the users of one cell are not separated by frequency or time.Different to FDMA or TDMA simultaneously they take place in the same frequencyrange. The users are separated by unique Codes. The Base Station and MobileStation must have common knowledge of the Codes used. The information of asingle user is spread up from a narrowband signal to a wideband signal using a high-frequency code (high so-called "chiprate"). This spread information is transmitted viaradio interface. After receiving the information, it is de-spread using the same code toregenerate the original information.

    The Codes in principal have orthogonal properties.

    frequency f

    time t

    power

    TS 1

    TS 2

    TS 3

    TDMA

    frequency f

    time t

    power

    1 2 3

    FDMA

    frequency f

    time t

    power

    1

    2

    3

    CDMA

    Multiple

    method

    BS & MS share

    knowledge about

    FDMA

    TDMA

    CDMA

    Frequency

    Time

    PN code

    P

    P P

    Multiple Access methods

    Fig. 11

    17

    Transmission Principles Siemens

  • Transmission via GSM Radio Interface Um

    A combination of FDMA and TDMA is used for GSM. The GSM physical channels aredefined by a pair of frequency bands (for UL and DL) and a Time Slot TS.

    FDMA in GSM

    In the GSM system, a band width of 200 kHz is defined for one frequency band.These HF channel widths are perfectly suited to the demands for speechtransmission.

    Allocation to (E-) GSM900, GSM-R, GSM1800 and GSM1900 is as follows:

    GSM900: (880) 890 - 915 MHz; 925 (935) - 960 MHz; 124 (174) channel pairs ;with a duplex distance of 45 MHz

    GSM-R: 876 - 880 MHz; 921 - 925 MHz; 19 channel pairs; with a duplex distanceof 45 MHz

    GSM1800:1710 - 1785 MHz; 1805 - 1880 MHz; 374 channel pairs; with a duplexdistance of 95 MHz

    GSM1900: 1850 - 1910 MHz; 1930 - 1990 MHz; common use along with otherstandards (e.g. IS-95; D-AMPS); with a duplex distance of 80 MHz

    In GSM for DL the higher and for UL the lower frequency range is used in general.

    Remark: In co-ordination with the frequency plan regulation, there is a 200 kHzprotective band inserted between the lower limit frequency and the first carrier ofevery sub-band, i.e. the corresponding channels are not used. This protective bandknown as the "guard band" is an accepted, virtually "unavoidable loss" for preventinginterference between different applications in the totally filled frequency range.

    18

    Transmission Principles Siemens

  • Transmission Principles Siemens

    FDMA in GSMGSM900 / 1800 Frequency Allocation

    C - Radio Frequency Channel (RFC)200 kHz

    UPLINK (UL) DOWNLINK (DL)

    Guard band

    (880) 890 MHz

    1710 MHz

    915 MHz

    1785 MHz

    (925) 935 MHz

    1805 MHz

    960 MHz GSM900

    1880 MHz GSM1800

    Duplex distance 45 MHz resp. 95 MHz

    25 (35) MHz

    75 MHz

    25 (35) MHz

    75 MHz

    Transmit bandof the Base Station

    C

    124

    (174)

    374

    C

    124'

    (174')

    374'

    C

    1

    C

    2

    C

    3

    C

    1'

    C

    2'

    C

    3'

    Transmit bandof the Mobile Station

    Fig. 12

    19

  • TDMA in GSM

    Each of the 200 kHz frequency bands is further sub-divided by TDMA into 8 so calledTime Slots TS. This produces 8 physical channels within one frequency band. InGSM a physical channel is thus defined by a determined frequency channel UplinkUL and Downlink DL and a determined time slot TS

    In the GSM system, up to 8 (with half-rate transmission even 16) calls can betransmitted "simultaneously" on one frequency band.

    A sequence of 8 time slots TS in one radio channel is referred to as a TDMA frame. ATDMA frame has a duration of 4.615 ms, an individual time slot a duration of approx.0.577 ms. The users data are transmitted virtually "piece by piece" on one specifictime slot every TDMA frame.

    GSM:combined

    FDMA/TDMA

    TDMA

    frame

    FDMA

    time

    frequency200 kHz

    0

    1

    3

    2

    4

    5

    7

    6

    1

    0

    1TS = 577 s

    1 TDMA frame =8 TS = 4.615 ms

    1TS = 577 s

    1 TDMA frame =8 TS = 4.615 ms

    Fig. 13

    20

    Transmission Principles Siemens

  • Transmission Principles Siemens

    3 GSM - Fixed Network Transmission

    PCMPulse Code

    Modulation

    speech band 1

    speech band 3

    speech band 2common line

    Multi-

    plexerband

    3 2 1

    1 0 1 1

    0 0 1 1

    A/D conversion

    1 1 0 0

    GSM - fixed network transmission

    Transmission Principles

    Fig. 14

    21

  • PCM30: Transmission in GSM fixed network part

    Information (conversations, data, signaling) is exclusively transmitted digitally viaPCM30 lines in the GSM-PLMNs fixed network part.

    Pulse Code Modulation - PCM

    Sampling values of a speech information are transmitted using binary code words(digitally) in PCM.

    Due to the digital structure of the message, the PCM signals are less susceptible tointerference than analogue signals. Regenerators reconstruct the original digitalsignal at the receiving end. Analogue signals, on the other hand, can only beamplified (including noise peaks).

    Amongst other things, during Pulse Code Modulation (PCM) an analogue oscillationis converted into a digital signal. A PCM signal can be transmitted alone or beembedded in a TDMA frame with other PCM signals (multiplexing).

    The conversion of an analogue telephone signal into a digital signal is carried out inthree steps:

    1. Band limitation: A bandpass filter restricts the incoming signal to the audiblefrequencies, i.e. to 300 to 3400 Hz.

    2. Sampling: Sampling values are taken at fixed intervals from the limited telephonesignal. The sampling frequency must be greater than twice the highest frequencywithin the analogue signal (Shannon Theorem). Internationally specified: 8000 Hz.

    3. 8-bit coding: Every amplitude value of the sampled (Pulse Amplitude Modulated -PAM) signal is transformed into an 8-bit word. The 8-bit word enables the analoguesignal to be represented in 256 quantization intervals.

    Since the transmission of an 8-bit word requires only a portion of the sampling

    interval (125 s) of the analogue signal, the 8-bit information is temporallymultiplexed (TDMA-procedure). 8 bits are transmitted in each time slot.

    Using PCM30 transmission systems, a total of 30 digital user values can betransmitted in the time frame of the sampling period of an analogue value, i.e. in 125

    s.

    22

    Transmission Principles Siemens

  • Transmission Principles Siemens

    1. Band limitation

    (300-3400 Hz)

    2. Sampling (8000 Hz)

    3. 8-bit coding

    Generation of a PCM Signal

    transmission of the coded

    sample value of signal 1

    coded sample value

    signal 2

    time slot

    0 1 0 0 1 1 0 1

    signal 1

    Fig. 15

    23

  • PCM30

    PCM30 transmission systems use digital transmission lines or radio relay. A PCM30frame consists of 32 time multiplexed time slots.

    The 32 time slots can contain pulse code modulated message information (speech,data) or signaling information in the form of 8-bit words.

    The total bit rate of a PCM30 line is 2048 kbit/s

    Time slot 0: alternately frame identification word and service word (alarms)

    Time slots 1-15 and 17-31: calls or data

    Time slot 16: signaling channel

    The pulse frames are transmitted in a direct sequence.

    PCM30: TDMA Principle

    telephone channels 1 - 15 telephone channels 17 - 31

    frame alignment/

    service word channelsignaling channel

    time

    slot

    PCM30PCM30

    pulse frame pulse frame pulse frame

    Fig. 16

    24

    Transmission Principles Siemens

  • Transmission Principles Siemens

    4 GSM Air Interface

    GSM Air Interface

    Advantage:

    mobility

    Single cell systems Cellular mobile communication systems

    Limits:

    1st generation 2nd generation incl. satellite roaming

    cell national GSM service area unlimited

    GSM (Ph1/2) (GSM Ph2+)

    Transmission Principles

    Fig. 17

    25

  • Radio Interface: Advantages, Problems and Solutions

    The air or radio interface, i.e. the connection between the MS and fixed networkcomponents, represents the fundamental difference to a fixed networktelecommunication system. The radio interface has its specific advantages, but alsoshows problems and disadvantages inherent to mobile communications.

    Advantage: Mobility

    The main advantage of mobile communications is the unrestricted mobility which canbe achieved only via a radio interface. Mobility was extremely restricted, especially inthe early years of mobile communications (one-cell systems). Mobility only reachedas far as the radio coverage between the MS and the transmission/receivinginstallations would allow. These limits were stretched significantly by cellular mobilecommunication networks of the first generation (since the early 1980s). Nationalborders and the degree of area coverage of a PLMN within a country formed theborders. In the GSM system, national borders no longer represented restrictions tomobility owing to inter-national roaming. It is still the case that nation-wideconnectivity is only offered around urban areas and along main traffic routes in largeareas of central Europe. Unlimited world-wide mobility is possible in co-operationbetween GSM and MSS such as Iridium, Globalstar and ICO.

    Problems & Solutions on the Radio Interface

    Cost Aspect: Problem - The need to built up a new network architecture withthousands of BTS. But: Compared with the costs for a fixed network ISDN / PSTNinfrastructure, a GSM PLMN is comparable cheap, because there is no need formillions of lines into every private household.

    Capacity: The capacity of transmission via radio interface is a great problem inmobile communications. Optimized usage of radio resources reducing the cellsizes, introducing sector cells and introducing the Hierarchical Cellular Structureswith Macro, Micro and Pico Cells solves this problem.

    Data Rate: GSM (Phase 1/2) offers a maximum 9.6 kbit/s, compared to the 64kbit/s of ISDN. Introduction of HSCSD, GPRS and EDGE enhances the GSM datarates significantly.

    Security Aspect: The radio interface can be intercepted with comparatively littletechnical expenditure. 1G could be intercepted without any problem, while thedigital transmission of the second generation offers protective measures againstinterception; the transmission is coded.

    Health Aspect: The mobile radio frequencies lie near the resonance frequency ofwater (2.45 GHz). In order to keep thermal exposure to the mobile radio user aslow as possible there are maximum power limitations for mobile phones, 2 W forGSM900 and 1 W for GSM1800.

    26

    Transmission Principles Siemens

  • Transmission Principles Siemens

    The Air Interface Um:Problems of radio transmission and possible solutions

    Cost Aspect:

    Capacity:

    Data Transmission Rate:

    Security Aspect:

    Health Aspect:

    Construction of mobile

    communication network

    cheaper than terrestrial network

    GSM900 / E-GSM: 124 / 174 frequency bands

    GSM1800: 374 frequency bands

    increasing subscriber numbers, data transmission

    Resource optimization / protection !!!

    GSM Ph1/2: 9.6 kbit/s

    Ph2+: HSCSD, GPRS, EDGE > 100 kbit/s

    Eavesdropping easy!

    GSM offers encryption

    H2O resonance frequency (2.45 GHz)

    Thermal load

    Pmax

    = 2 / 1 W (GSM900/1800)

    Fig. 18

    27

  • Problems of Physical Transmission

    Screening: If there are hindrances between transmitter and receiver, the signalswill weaken. A connection can thus become problematic or impossible. In GSMthere is therefore the possibility of regulation of the transmitting power (PowerControl - PC) from mobile and base stations over several orders of magnitude.

    Multipath Propagation: Multipath propagation through reflection and dispersionof radio waves leads to phase-shifted reception of signals of different paths. Theinterference can distort, amplify or erase the signal. An attempt to compensate fornegative effects of multipath propagation is given by power control, frequencyhopping, two antenna receivers for the base station (antenna diversity) andredundancy of the transmitted information.

    Distance MS - BTS: The distance between MS and BTS has proved to beproblematic in several ways. The receive power sinks with increasing distancebetween transmitter and receiver theoretically with the square of the distance.Various physical effects such as atmospheric attenuation (weather-dependent)reduce the receive power even more. This attenuation depends on the frequencyand increases with increasing frequency in mobile radio relevant frequencyranges. The distance furthermore causes a reception de-lay, which may lead tointerference between neighboring time slots in TDMA. GSM responds to this delayby means of a regulation of the transmission time (Timing Advance TA). GSM900cells (GSM Phase 1/2) are limited to maximum 35 km, GSM1800 cells tomaximum 8 km radius as a result of the distance-related problems. There is thepossibility in GSM Phase 2+ to realize "Extended Range Cells" with a maximumradius of 100 km for GSM900.

    MS Speed: Moving mobile stations can cause transmission distortions due toDoppler effect. A compensation for this effect up to a maximum speed of 250 km/h(130 km/h), for GSM-R a more powerful compensation for speeds of up to 450km/h was deloped.

    Interference with external systems: The receive quality can also be disturbed byelectromagnetic waves from outside systems (e.g. car ignition, generators, PCs).A compensation is being tried out by means of the mechanisms described undermultipath propagation.

    28

    Transmission Principles Siemens

  • Transmission Principles Siemens

    Radio Transmission: Physical Disturbances

    Mobility

    Screening

    Multipath propagation

    Distance MS-BS

    MS speed

    External system interferencetransmitted signal

    received

    signals

    signal to

    antenna

    Digital systems offer manyerror recognition and

    correction mechanisms( redundancy)

    signal attenuation (Power Control PC) interference (PC, f-hopping, diversity, regeneration) power loss (f-dep.); delay (PC, TA, cell size) Doppler effect (corrections) quality loss (PC, f-hopping, regeneration)

    Fig. 19

    29

  • Frequency Resources: Optimized Utilization

    In order to be able to keep up with the increasing demands on mobilecommunications despite the limited resources of the radio interface differentapproaches are being pursued.

    Additional Frequency Ranges: The simplest way to cope with the growingdemand for mobile communications is to expand the available frequency range.This approach was pursued with E-GSM and GSM1800. Any further futureexpansion would be problematic as other frequency ranges are already reservedfor other applications.

    Speech Compression: Speech compression in GSM allows a reduction of voiceinformation from 64 kbit/s to 13 kbit/s in the so-called Full Rate FR speech and to5.6 kbit/s with the Half Rate HR speech. HR speech thus leads to a considerableincrease in capacity. Central aspects of HR speech are described in the GSM Rec.06.02, 06.20 - 22, 06.41 and 06.42.

    Cell Size Reduction/Coverage: The most important measure for